Large DC arc furnaces equipped with one (1) or more bottom electrodes require a significant amount of furnace down time to maintain and/or repair the bottom electrode(s). Typically, this repair can take sixteen (16) to twenty-four (24) hours of furnace downtime every 1500 heats, which results in a considerable loss in furnace production.
The bottom electrode of a DC arc furnace must be replaced every 1000 to 2000 heats. Presently the normal bottom electrode exchange procedure occurs at the furnace. This bottom electrode procedure may take from 12 to 24 hours during which time production is lost. The on-furnace exchange procedure is outline below.
1) The furnace is drained of all metal and allowed to cool for several hours. PA1 2) A digging machine is placed on the furnace upper shell. This digging machine has a pneumatic jack hammer which is articulated on an arm which can pivot 360 degrees. The digging device is used to loosen the refractory material in the slip joint between the bottom electrode refractory and the shell refractory. This digging process may take an additional hour or two. PA1 3) The power connections along with air and/or water connections to the bottom electrode must be disconnected. PA1 4) A portable bottom electrode push-up device is placed on the ladle car and driven underneath the furnace vessel. This push-up device consists of a cylindrical metal fabrication called the push-up head which aligns with the lower perimeter of the bottom electrode. This push-up head is raised up to the bottom electrode by a large bore hydraulic cylinder. This cylinder develops several hundred tons of force to break the bottom electrode free of the hearth refractory and lift it to an elevation where it can be secured with a sling and lifted out of the vessel by overhead crane. PA1 5) Any refractory loosened or damaged when the bottom electrode was pushed out is repaired. Areas of worn refractory are built back up to the proper thickness. PA1 6) A new or re-built bottom electrode is lowered into the vessel and aligned so that all of the power, air and/or water connections can be re-connected. PA1 7) The slip joint between the shell refractory and the bottom electrode refractory is filled with a ramming mix and tamped down. PA1 8) The bottom electrode push-up device is removed from underneath the furnace. PA1 9) The furnace is re-started.
The present invention utilizes an off-furnace bottom electrode exchange. The basic idea of an off-furnace bottom electrode exchange is to minimize the amount of production time lost. This is accomplished by having a spare furnace shell with a new or re-built bottom electrode already in place. Also, other maintenance to the furnace shell such as tap hole exchanges and water cooled panel repair or replacement can be done off-line saving additional downtime. In addition to limiting down time the maintenance work can be stretched out over a longer period of time providing scheduling flexibility, time for higher quality work, and possibly reducing or eliminating maintenance overtime.